Physics notes

• Frequency

  The number of waves passing a point per second

  
• Longitudinal waves


  • Vibrations are parallel to the direction of energy transfer

  
• Reflection

  Waves hit an object, such as a barrier, and are reflected

  
• Diffraction


  1. Waves pass through a narrow gap and spread out

  2. As the gap gets bigger, the effect gradually gets less pronounced

  
• Angle of incidence = angle of reflection

  
• The image in a mirror is the same size as the object and the same distance directly in line with the object
• Refraction

  1. When waves enter a different medium, their speed can change

  2. Wavelength can increase or decrease

  3. Waves can change direction

  
• When light is moving from a denser medium towards a less dense one, most of the light is refracted, but a small amount of it can be internally reflected

  
• Monochromatic light


  Light of a single wavelength (a single colour)
• Electromagnetic spectrum

  • Radio waves
  • Microwaves
  • Infrared
  • Visible light
  • Ultraviolet
  • X-rays
  • Gamma rays

  
• Properties of electromagnetic waves

  • They are all transverse
  • They can all travel through a vacuum
  • They all travel at the same speed in a vacuum (3 x 10^8 m/s)

  
• Compression

  A place where the molecules are bunched together
• Rarefaction

  A place where the molecules are spread out
• Ultrasound

  Sound waves with a frequency greater than 20,000 Hz
• Hearing range

  Humans can hear sounds between about 20 Hz and 20,000 Hz
• Amplitude

  Greater amplitude = louder sound
• Frequency

  Greater frequency = higher pitch
• Solids


  • Molecules are very close together and arranged in a regular pattern
  • Molecules vibrate about fixed positions
• Gases


  • Molecules are widely separated
  • Molecules move about randomly at high speeds
• Evaporation


  More energetic molecules near the surface of the liquid have enough energy to escape, causing the liquid to change to a gas
• When evaporation occurs, energy is lost from the liquid, causing the average energy of the remaining molecules to decrease and the temperature to decrease
• Brownian motion


  Small particles suspended in a liquid or gas move around randomly due to collisions with fast-moving molecules
• Temperature of a gas

  Related to the average speed of the molecules: The hotter the gas, the faster the molecules move
• Pressure


  Caused by the force of gas molecules colliding with the walls of their container
• Thermal expansion

  When materials are heated, the molecules start to move around faster, causing them to knock into each other and push each other apart, making the material expand
• Conduction

  When a substance is heated, the atoms start to vibrate more, transferring energy from atom to atom
• Metals


  • Extremely good at conducting heat
• Non-metals

  • Poor at conducting heat, called insulators
• Convection


  The main way that heat travels through liquids and gases, where hot, less dense material rises and is replaced by cooler, denser material
• Radiation


  The only way heat can travel through a vacuum, as part of the electromagnetic spectrum (infrared)
• Whenever energy is transformed, some of the original energy usually ends up in an unwanted (wasted) form, usually in the form of heat, light or sound
• The law of conservation of energy: Energy cannot be created or destroyed, it can only change from one form to another
• Density


  The mass per unit volume of a material
• Renewable energy resource


  One that is replenished at a faster rate than the rate at which it is being used, so it cannot run out
• Reliable energy resource


  One that can produce energy at any time
• Energy resources not from the Sun


  • Geothermal
  • Nuclear
  • Tidal
• Sound waves consist of vibrating molecules and are a type of longitudinal wave

  
• Types of waves:

  • transverse
  • longitudinal
• Transverse waves

  • vibrations are at 90 degrees to direction of energy transfer

  
• Liquids

  • molecules are still close together (no gaps) but are no longer arranged in regular pattern (lattice structure)
  • molecules are still able to slide past each other